The Pete Townshend-penned “Who Are You” already provides the opening soundtrack for “CSI” on CBS — and now Townshend is actually writing an original song for a TV series.

The legendary Who guitarist/frontman has co-written (with Nathan Barr) “It Must Be Done,” which will be featured on the April 30 episode of “The Americans” (10 p.m. on FX).

Townshend isn’t the first member of The Who to dabble in TV; lead singer Roger Daltrey has appeared in several shows (“Sliders,” “Highlander,” “Pirate Tales”). And, back in 1997, I interviewed Who bassist John Entwistle, who was writing the music for a Fox cartoon series called “Van-Pires.” (That interview was like pulling teeth — I still break out in flop-sweat just thinking about it.) Entwistle died in 2002.

Townshend recently signed a deal with Spirit Music Group, which has a relationship with PJ Bloom, the music supervisor for “The Americans.”

“When I signed my deal with Spirit I was hoping we could do stuff differently and working with Nate [Barr] was extremely gratifying and artistically exciting,” Townshend said in a statement.

Good ‘News’ for Sawyer

ABC’s “World News” has become the first network evening newscast to reach 1 million “likes” on Facebook — and it’s the only nightly newscast (ABC, CBS, NBC) that’s up, year-to-year, in the “money” demo of adults 25 to 54 (2.2 million viewers for the season through March 30 — a 5 percent increase over last year). Diane Sawyer anchors.

Meanwhile, Animal Planet’s season opener of “River Monsters” Sunday night drew 1.7 million viewers — the most-watched season debut in the network’s history. The show’s hosted by Jeremy Wade.